Apparatus for the determination of flammability and smoke density of polymers

ABSTRACT

There is disclosed a method and an apparatus for determining the flammability and smoke density of polymeric materials. The apparatus comprises a first device to determine the flammability of the polymer under consideration by the oxygen index method and a second device connected to said first device to determine simultaneously, if desired, the smoke density of the same polymer.

United States Patent 1 1 Di Pietro et al.

Inventors: Joseph Di Pietro; Heinrich E.

Stepniczka, both of Alma, Mich.

Assignee: Michigan Chemical Corporation, St.

Louis, Mich.

Filed: Apr. 28, 1972 APE-2 3535 1549.

Continuation of Ser. No. 73,772, Sept. 2|, 1970, aban l qn g W US. Cl. 23/253 PC, 356/36, 356/207 Int. Cl.. G0ln 21/12, G0ln 21/26, G0ln 31/12 58 Field r Search 23/230 PC, 253 PC; 356/36,

[451 May 21, 1974 3,469,945 9/1969 Delassus et a1. 23/253 PC X 3,498,721 3/1970 Thorndike 250/218 X OTHER PUBLICATIONS Standard Method of Test for Flammability of Plastics Using the Oxygen Index Method, ASTM Designation D2863-70, p. 719-722 (May 8, 1970).

Primary Examiner-Joseph Scovronek Attorney, Agent, or Firm-James J. Mullen [57] ABSTRACT There is disclosed a method and an apparatus for determining the flammability and smoke density of polymeric materials. The apparatus comprises a first device to determine the flammability of the polymer under consideration by the oxygen index method and a second device connected to said first device to determine simultaneously, if desired, the smoke density of the same polymer.

[56] 7 References Cited 5 Claims, 1 Drawing Figure UNITED STATES PATENTS 3,544,218 12/1970 Cassidy 356/207. X

s% 02 L a 0 o pected penetration will depend, however, on resolving a number of difficulties related to safety. Two of these difficulties appear quite significant. The first is the flammability of plastics and the dangers associated therewith; the second is the degree of smoke generation while the plastic material is burning. In this connection it should be stated that concern shown by the public at large and by legislators, consumer advocates and industrial organizations over the two difficulties mentioned above has reached a high level. Thus research activities and manufacturing efforts in the field of flame retarding plastic materials have been accorded high priority. Similarly, studies have been made on the mechanism, composition and generation of smoke as well as methods for determining these properties. It is quite apparent that the nature of these studies is complicated and sometimes based on theoretical evaluations.

I The behavior and/or mechanism of flame retarding agents during the process of burning is often explainedin terms related to the formation of smoke as means for quenching the flame or, perhaps, preventing the formation of the flame itself. In fact it has been suggested that the density of smoke generated by burning some plastic materials would be higher when said materials had been rendered fire retardant. Thus it has become increasingly important to evaluate both flammability and smoke density of polymeric materials which are'destined for consumer use.

Many methods and tests for determining the flammability of organic polymeric materials have been devised. Because the intended uses of the tested polymers varied considerably, the'flammability tests were qualitative and empirical in nature. However, quantitative and reproducible results became available with the introduction of the Candle Test employing the Limiting Oxygen Index method, now known as the Oxygen Index which 'is defined as the minimum volume-fraction of oxygen in an atmosphereof oxygen and nitrogen which is needed to sustain the candle-like burning of a polymeric specimen. The Oxygen Index method is now recognized for use on plastic materials by the American Society for Testing and Materials (ASTM) of 1916 Race Street, Philadelphia, Pa. 19103, and said test method has been given the designation D 2863-70 (see Annual Book of ASTM Standards effective May 8, 1970). For further explanation and theoretical discussion on the Oxygen Index, reference is made to a paper by J. DiPietro and H. Stepniczka presented at the Society of Plastic Engineers Conference,New York, N.Y.,

2 May 6, 1970, and published in Plastic Engineer Society Inc., Volume XVI, pp. 463-68.

Many laboratory methods have been devised for measuring the burning characteristics of various materials. Some of these methods have included procedures for measuring smoke development but the data secured by these test methods have suffered from lack of correlation with practical fire conditions. Furthermore the methods have not been suitable for testing many materials in' the form in which they are used in actual applications. I

The present invention is concerned with the measurement of the amount of smoke evolved from the burning, in a controlled atmosphere, of plastic materialslikely to be used in many consumer applications. Of considerable importance was the matter of evaluating the effects of certain flame retardant additives on the smoke density and correlating the data obtained to the flammability tests.

Measurements of smoke and/or smoke density can be generally accomplished in two ways. One is to measure light transmittance through smoke itself and the other is to collect the smoke particles on a suitable filter paper which can be weighed or measured for light transmittance. The most common method for the determination of smoke employs a light source and a photoelectric cell, arranged so that the electrical output of the cell may be used as a measure of the attenuation of light by smoke. The electrical outputs recorded as light transmittance curves provide a means for determining the smokes optical density based on Beers law, see cr ss taasm.r i a en TB-Az2 9 2).

marily the advantages of the apparatus of the present invention lie in providing the tester with the ability to conduct the measurement of these determinations under a variety of conditions. It is believed that data relating to the determination of smoke density at, or below, the Oxygen Index level are quite significant.

Other objects and advantages of the invention will become more apparent from the following description taken in conjunction with the accompanying drawing which depicts a schematic representation in crosssection of the apparatus of the invention. In particular, numerals l0 and 12 refer to points linking the apparatus to sources of oxygen gas and nitrogen gas, respectively. Lines 10 and 12 are provided with filters (not shown) to ensure that the gas stream is free of small particulate matter. It has been found that fifteen micron in-line filters are adequate. Numerals l4 and 16 represent shut-off valves, while 18 and 20 refer to fine metering valves. These valves can be of various designs and no preference is made as to the exact structure of these valves. The important aspect is to provide a means to dispense and regulate the gas flow in such a manner as to keep the operation of flowmeters 22 and 24 under control. Flowmeters 22 and 24 are, of course,

calibrated and standardized to provide corrections for changes in atmospheric conditions. At point 26 the two gases meet to form one line which leads to the bottom of the main body of the apparatus comprising two chambers defined by walls 37 and 39 which have similar dimensions but of course, if desired, the two chambers can be of difierent sizes. The gaseous mixture enters chamber 37 at point 28. A bed of glass beads 30 or similar material to effect good and intimate mixing is provided. Now the thoroughly mixed gaseous stream comprising the oxygen and nitrogen emerges through tube 31 at the top of which there is located the holder 32 of the polymeric sample 34 under study. A concentric heating coil 36 is provided on the inner wall of burning chamber 37 as a source of heat for pyrolytic studies on the polymeric sample. Another arrangement is to heat the gaseous mixture itself before coming in contact with the sample. The temperature of the sample and the area surrounding it is continuously recorded by a suitable temperature measuring device (not shown). Of course the temperature may be observed periodically through use of an appropriate thermometer or any similar device such as a set of thermocouples connected to a calibrated reader. Chamber 39 is situated directly on top of burning chamber 37. A workable arrangement can be made in which the walls at the top of chamber 37 are provided with a well capable of receiving metal inserts extending fromthe bottom of chamber 39 so that the walls forming the two chambers can be firmly secured to each other permitting the chamber 39 to continue from the chamber 37. The plate or platform 38 is an optional arrangement the purpose of which is providing a means to reduce the area between the two chambers. Numerals 40 and 42 are optical members, a light source and a photocell, respectively to measure the light transmission through chamber 39. The camera 44 is an optional member which can be used to photograph the evolved smoke and particularly the particles making up the smoke. Exit 46 is generally connected to a chimney but can also provide a holder which can contain a filter device. This is an optional arrangement to measure smoke density by filtering a known volume of gas through a known area of the filter, and the resultant spot is classified according to its degree of blackness.

In determining the flammability and smoke density of a particular polymeric system, a sample having the dimensions of /sinch X linch linch is placed in holder 32 which has a square shape adjustable to the size of the sample. The flammability of the same is determined by the Oxygen lndex method described hereinbefore.

Oxygen and nitrogen are supplied through lines and 12, respectively. Now valves 14, 16 and 18, are adjusted so that a definite rate of each gas is established and equilibrated. Generally a gas flow of 300 cc per second is used. The recommended range is 219 to 876 cc per second. The gas flow refers to the gaseous mixture comprising the oxygen and nitrogen as supplied to the specimen through tubing 31. Before ignition the apparatus is purged with the particular gaseous mixture for about 60 seconds to insure, at least, that the gas composition within the burning chamber is the same as that of the subsequent gas stream supplied for burning. Now the polymeric specimen is ignited with a torch, normally a propane torch. Actually any igniting means capable of supplying a flame is satisfactory. 1f the specimen commences to burn it indicates that the gaseous mixture supplied to the specimen through 31 is of a composition that is conducive to support the burning of said specimen. The oxygen fine-metering valve 18 is manipulated to give minimum oxygen amounts. Thus the volume-fraction of oxygen is noted for calculating the Oxygen lndex.

While the specimen is burning any resulting smoke will travel to chamber 39 where photocell 42 measures the degree of light transmission from light source 40 across the chamber 39. Of course the photocell is calibrated prior to each run to insure that the dark current of the phototube (not shown) is accounted for. Often, it is desirable to know the shape and the size of the smoke particles, and camera with lens 44 is provided for that purpose.

The shapes of chambers 37 and 39 are not critical; they can be cylindrical if desired. The walls of chamber 37 are preferably transparent to allow visual observation of the burning. Actually only a section of the wall need be transparent and it can be effectively a glass window. The glass, of course, should be heat resistant such as a borosilicate glass. As to the walls of chamber 39 it is sometimes desirable that the light source and the photocell be mounted within the walls with longitudinal adjustment. This is to enable the observation and- /or measurement of smoke at various heights or levels of the chamber. At this juncture mention should be made of the fact that the walls of chamber 39 be made of a material resistant to corrosion, and particularly to chlorine or bromine which are found in almost all fire retarding agents. Of course, the entire apparatus is insulated to maintain temperature and light control; the insulation being provided by a suitable external housing (not shown).

The versatile features of the apparatus of the present invention can be appreciated when it is realized that the Oxygen Index (0.1.) of a particular polymer system can be measured at various specimen temperatures including ambient or different gas mixture temperatures and also determined is the smoke density of the system at each temperature. For example, some speculations and postulations regarding changes in the value of the Oxygen Index with respect'to changes in temperature were confirmed to the extent that the temperature of the sample itself was responsible for these changes and not the temperatures of the gas or environment surrounding the sample. Table I below shows the changes in the values of the Oxygen Index when the polymeric sample under investigation is heated to high temperatures. The polymers tested were untreated and fire retardant (F.R.) acrylonitrile butadienestyrene (ABS), polyester and polystyrene. Also provided in the Table are the amounts of bromine (as Br) contributed from the fire retarding agent.

TABLE 1 OXYGEN lNDEX AT DIFFERENT SAMPLE TEMPERATURES they maintain this smoke density for the entire burning period.'lf the gaseous mixture has slightly more oxygen than indicated by the samples 0.]. value, the sample will burn, generating the maximum smoke density, until the sample is consumed to a point of less than I incl square (6.45cm) burning area, at which point the smoke density decreases. Samples with and percent Br levels, however, build up a char-like material during the combustion process which increases with increasing time until it covers most of the burning area, thus decreasing the burning area as well as the smoke density. The effect that the smoke density of highly flame retarded systems goes through a maximum and decreases within a 3 minute period has been observed in these three systems studied here.

Table II shows percent of light absorption and the maximum optical smoke density generated by these systems. As anticipated, the smoke density increased with an increasing amount of flame retardants used in the system; however, if the amount of oxygen in the gaseous mixture is set at the 0.1. value of the untreated sample, then the flame. retarded sample does not generate as' much smoke as the untreated one. (See Table III) TABLE II SMOKE DENSITY OF DIFFERENT POLYMER SYSTEMS AT AMBIENT TEMPERATURE The samples in Table I] had areas of one inch'square exposed to the flame. The gas flow was 300 cc/sec at ambient temperatures and the light path in the second chamber measured 6 in. (1 5 ern) 'lhe smoke density was measured utilizing the formula D log (l /l,) (cl/2.303) Optical density of smoke Drn maximum smoke density measured.

Wherein I0 Initial lists. in ns y l, Emergent light intensity l= Length of light path a ..Z EQFPEBPSFREEEE L TABLE III SMOKE DENSITY OF BURNING ABS AT DIFFERENT LEVELS OF FLAME RETARDANT AND AT A CONSTANT O.l. OF 0183"" Percent Light Maximum Optical System Absorption Smoke Density ABS, virgin material 92 1.10 F.R. ABS, 5% Br 43" 0.23 F.R. ABS, 10% Br 0"" 0.00 F.R. ABS, l5i: Br 0" 0.00

(a) O.l. of untreated ABS sample.

(b) The flame extinguished after 37 seconds; maximum light absorption after 15 seconds (at first measurement when chamber was installed above the combustion chimney of the Flammability Index Tester).

(c) No ignition at this O.l. value.

In view of the .above it is seen that the apparatus of the invention will assist the researchers in the field of flame retardants in providing better and more suitable materials than now available. Further the apparatus will help standardize the methods of evaluating many consumer products such as fabrics, carpeting, furniture and the like.

As various changes could be made in the construction of the apparatus of the invention without departing from its scope, it is intended that the above description in conjunction with the accompanying drawing shall be interpreted as illustrative and not limitative.

What is claimed is:

1. An apparatus for determining the flammability and smoke density of an organic polymer material comprising in combination a first chamber containing means to support a sample of said polymer, metering devices for supplying variable amounts of oxygen and nitrogen to said chamber, a diffuser adapted to form an intimately mixed stream of said gases in which said polymer material is caused to burn, said first chamber also containing a heating device for conducting the burning of the polymers at various environmental temperatures, and a second chamber contiguous with said first chamber whereby said gases pass through said first chamber into said second chamber, said second chamber including an optical system for measuring the density of smoke evolving from the burning of said polymer material.

2.'An apparatus as described in claim 1 wherein said optical system comprises a light source and a photocell.

3. An apparatus as described in claim 1 wherein said second chamber contains a device for photographing the smoke evolved from burning the polymer.

4. An apparatus as described in claim 1 wherein said heating device is a heating coil.

5. An apparatus as described in claim 2 wherein said light source and photocell are slidably mounted on the walls defining said second chamber. 

2. An apparatus as described in claim 1 wherein said optical system comprises a light source and a photocell.
 3. An apparatus as described in claim 1 wherein said second chamber contains a device for photographing the smoke evolved from burning the polymer.
 4. An apparatus as described in claim 1 wherein said heating device is a heating coil.
 5. An apparatus as described in claim 2 wherein said light source and photocell are slidably mounted on the walls defining said second chamber. 